The invention is based on a priority application DE 101 23 193.8 which is hereby incorporated by reference.
This invention relates to a method of transmitting data at a time-variable data rate as set forth in the preamble of claim 1, to a communications module for a user terminal for carrying out such data transmission as set forth in the preamble of claim 8, and to a connection control module for a network facility of a network for carrying out such data transmission as set forth in the preamble of claim 10.
In the case of telephone networks it is known that a user terminal, such as a telephone set, establishes a connection to a communication partner, such as a second telephone set, through the telephone network, with a guaranteed data rate being made available for the connection. If the connection is set up through an integrated services digital network (ISDN), for example, at least one B channel with usually 64 kb/s is provided for the connection, so that a data rate sufficient for voice transmission is available. The telephone network reserves the data rate for the connection irrespective of whether it is actually used. The connection is also maintained during pauses in the conversation, for example.
A similar situation results if a connection is established from a user terminal, e.g., a personal computer, over a telephone network to the Internet. Even if the capacity of the connection through the telephone network is not fully utilized by data being transmitted from the Internet to the user terminal or vice versa, for example because a bottleneck occurs in the Internet, the telephone network will make available a constant guaranteed data rate for the connection between user terminal and Internet.
Accordingly, the capacity of a telephone network must be designed for a peak load, the maximum traffic experienced by the network.
In packet-oriented data networks, particularly in connectionless data networks, the initial situation in this respect is different. Such data networks are inherently flexible in terms the type of data to be transmitted or the bandwidth made available to a user, so that their capacity can be optimally utilized. If more data packets have to be transmitted than can currently be handled by the data network, these packets will be buffered at the user end and/or in the network or discarded until sufficient transmission capacity is available again.
When a user is “surfing” on the Internet with an Internet browser and only retrieving text and video data from the Internet or sending individual control commands, e.g., requests for such video data, to the Internet, time delays due to insufficient transmission capacity of the Internet and/or of an access network to the Internet are not particularly annoying to the user. A somewhat slower picture setup in the browser or a slightly delayed response to a request for data from the Internet is generally acceptable.
Things are different, for example, if the user retrieves a video sequence or speech data from the Internet or wants to send such information to the Internet. If, in that case, too little transmission capacity is made available to the user, i.e., if the data rate during transmission is too low, this may result in interrupted and/or torn video or speech sequences.